Taxanes

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Chapter: Essential pharmacology : Anticancer Drugs

Paclitaxel : It is a complex diterpin taxane obtained from bark of the Western yew tree, which exerts cytotoxic action by a novel mechanism. It enhances


TAXANES

 

Paclitaxel

 

It is a complex diterpin taxane obtained from bark of the Western yew tree, which exerts cytotoxic action by a novel mechanism. It enhances polymerization of tubulin: a mechanism opposite to that of vinca alkaloids. The microtubules are stabilized and their depolymerization is prevented. This stability results in inhibition of normal dynamic reorganization of the microtubule network that is essential for vital interphase and mitotic functions. Abnormal arrays or ‘bundles’ of microtubules are produced throughout the cell cycle. Cytotoxic action of paclitaxel emphasizes the importance of tubulin-microtubule dynamic equilibrium.

 

The approved indications of paclitaxel are metastatic ovarian and breast carcinoma after failure of first line chemotherapy and relapse cases. It has also shown efficacy in advanced cases of head and neck cancer, small cell lung cancer, esophageal adenocarcinoma and hormone refractory prostate cancer.

 

Dose: 175 mg/m2 by i.v. infusion over 3 hr, repeated every 3 weeks.

 

INTAXEL, PAXTAL 30 mg in 5 ml cremophor emulsion (polyoxyethylated castor oil + alcohol + water) per vial. Acute anaphylactoid reactions occur because of the cremophor solvent. Pretreatment with dexamethasone, H1 and H2 antihistaminics is routinely used to suppress the reaction.

 

The major toxicity is reversible myelosuppression and ‘stocking and glove’ neuropathy. Chest pain, arthralgia, myalgia, mucositis and edema can be troublesome.

 

Docetaxel

 

More potent congener of paclitaxel with the same mechanism of action. It has been found effective in breast and ovarian cancer refractory to first line drugs. Small cell cancer lung, pancreatic, gastric and head/neck carcinomas are the other indications. Major toxicity is neutropenia, but neuropathy is less frequent. Arrhythmias, fall in BP and heart failure are also reported.

 

Dose: 100 mg/m2 i.v. over 1 hr; repeat at 3 weeks.

 

DAXOTEL 20 mg, 80 mg inj.

 

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